I didnt know where I wanted to mount my gauges and one day I was holding up some copper for the intercooler and I had it up by the tank. Just then I started measuring ID on the copper and the OD on some gauges and found some to fit perfectly into the elbows. In the upper left is my ATF Gauge, Lower left is my Boost pressure, Upper right is oil psi, Lower right is Fuel pressure The three small gauges are 1.5" and the larger gauge is a 2" I think once I do final paint and polish it is really going to pop. Plus the gauges are in a great place to see while riding instead of being hidden down on the side of the bike or something..